1. Field of the Invention
This invention relates to a power supply system and a starting method thereof. More particularly this invention relates to a power supply system in which a large amount of current is required to be controlled with a quick response time and a starting method thereof.
2. Discussion of Background
As an example of a conventional power supply system, a power supply system for a coil to be used for nuclear fusion where a large amount of current is required will be described below.
When generating plasma for nuclear fusion, it is required to control with quick response a current of a coil for use in plasma position control so as to control a position of a plasma. To meet this requirement, there should be provided a power supply system capable of controlling a large amount of current with a high voltage.
Hitherto, for such a power supply system, there has been used a power supply system provided with a controlled rectifier connected in series to a diode rectifier as shown in, for example Japanese Patent Disclosure No. 55-125080. In the conventional power supply system, when increasing the plasma current to several tens of kA, a DC voltage of, for example about 20 kv is generated, and when the plasma current becomes constant and the coil current for plasma position control also becomes constant, an AC side interrupter for a diode rectifier is opened, and thereafter the coil current for plasma position control is controlled by a controlled rectifier rated at several kv.
However, the conventional power supply system has the disadvantage that when the AC side interrupter for the diode rectifier is opened, a drastically large load fluctuation is generated if observed from the AC power system, resulting in an extremely large disturbance on the AC bus line. In addition, a diode rectifier with ratings of 10 kv or more and several tens kA becomes necessary and this results in high cost. Particularly in a medium scale nuclear fusion system, when there is no motor-generator on the AC side and AC power is directly fed to the power supply system from a commercial power source, it is not allowed to produce a large load fluctuation at one time. So that there has been necessiated such a power supply system in which all of the current control is performed only by a large capacity controlled rectifier, or in which several diode rectifier units are connected in series to a controlled rectifier so that a plurality of AC interrupters for a plurality of diode rectifiers are sequentially opened, which causes the power supply system to be extremely expensive.